The present invention relates generally to systems and methods for controlling illumination in a plurality of defined areas. More particularly, the present invention relates to a network of occupancy sensors capable of detecting a human presence and a network lighting controller for regulating illumination levels in a plurality of defined areas based on detected occupancy.
The use of occupancy sensors in lighting control has been on a steady increase as the industry advances towards more drastic energy conservation measures. Conventional occupancy sensors utilize various detection methods for detecting occupancy in a defined area. Among the known methods, passive infrared (PIR), microwave Doppler shift, ultrasonic Doppler shift and sound sensors are the most common.
Passive infrared (PIR) sensors are considered to be the most common type of occupancy sensor. They are able to “see” heat emitted by occupants. Triggering occurs when a change in infrared levels is detected—for example when a warm object moves into or out of view with respect to the sensor's eyes. PIR sensors are very resistant to false triggering. Although some PIR sensors have an operating range of up to 35 feet in specific directions under ideal conditions, they are most reliable within a 15-foot range. This is due to the blind spots between their wedge-shaped sensory patterns becoming wider with distance. The sensor is most sensitive to movement laterally across the field of view. They are passive—they do not send out any signal- and depend on the intensity of the heat from the moving part of the subject, which attenuates by the square of the distance.
PIR occupancy sensors typically use PIR elements with two to six sensing areas. The Fresnel lenses focus a projection of the defined area on the PIR element. The output of each sensing area on the PIR element is amplified electronically. Differential amplification is used so that a higher common-mode rejection ratio (CMRR) may be achieved. The CMRR measures the tendency of a device to reject input signals common to both input leads, and is defined as the ratio of the powers of the differential gain over the common-mode gain, as measured in positive decibels. In other words, differences between values of different sensing areas of the PIR element are amplified and the common factor, which is present due to IR emissions from other surfaces and objects, is rejected in the amplifier. Thus, once a heat-emitting source crosses the sensitive areas, the projection is drifted from one PIR area to another. This will result in a pulse at the output of the amplifier. The pulse is then compared to a desired threshold to filter the effect of thermal and electronic noises. Various coverage patterns could be achieved via modifications to the construction of the Fresnel lens.
There has been an extensive amount of research and development conducted to implement and improve performance and accuracy of occupancy detection. Accordingly, various sensing technologies employ two or more detection methods in a single system in order to reduce false tripping. Dual technology occupancy sensors generally use an active sensing method in combination with a PIR element. Microwave and ultrasound are the most widely used technologies. Both methods rely on processing Doppler shifts between the frequency of the transmitted and reflected signals.
To achieve a completely passive dual technology sensor, a design as previously known in the art employs a PIR sensor as the main detector and a microphone as a second detector. This enhances the accuracy of the sensor through detecting spontaneous changes in the amplitude of the noise in the defined area. The signal from the microphone is amplified by an automatic gain control amplifier, and accordingly consistent background noises are filtered out. The microphone module is activated by the PIR module, or in other words the lights will be turned on once the PIR element senses a motion. Once in the ON state, either one of the PIR or microphone modules will keep the lights in the ON state. Once motion has not been sensed for a predetermined period of time (timeout), the lights will be put into the OFF state and a grace period timer will start. During this period, the lights could be reverted into the ON state by a signal from the microphone as well as from the PIR module. Once in the OFF state, the microphone will not regulate the lights into the ON state. It is the PIR module that reinitiates the ON state and also activates the microphone.
However, occupancy sensors and associated systems or networks as are conventionally known in the art still typically share a common failure with regards to false triggering of the various sensors. For example, sensors may fail to detect occupants and trigger the lights off while the area is still occupied. Ambient noise in a defined area may also be an issue for conventional systems, particularly infrequent sounds which are not necessarily cyclical and thereby easily distinguishable from occupancy in the area. In addition, where an array of microphones is used to detect sound in the defined area but the received sound signals are collectively analyzed as is typically known in the art, cross-correlation of the signals may be relatively low.